This invention relates generally to digital memory systems and more particularly to digital memory systems adapted to store samples of received radio frequency signals and to enable subsequent retransmission of such received radio frequency signals from the stored samples.
As is known in the art, it is frequently desired to digitally store samples of a received radio frequency signal and later reconstruct such radio frequency signal from such stored samples for retransmission. In one such system the received signal is periodically sampled at or above the Nyquist sampling rate, each sample is next converted into a corresponding digital word, and each digital word is then stored in a digital memory. When it is desired to retransmit the radio frequency signal, the stored digital words are sequentially read from the memory in the sequence in which they were stored, such read digital words are converted into corresponding voltages to produce a radio frequency signal which is then amplified and retransmitted.
With such arrangement the degree to which the retransmitted signal resembles the received radio frequency signals depends, inter alia, on sampling the received radio frequency signal at a rate at, or above, the Nyquist sampling rate. Consequently, in a system which is required to process received signals having frequencies within a predetermined bandwidth the received signal would typically be processed through a pair of quadrature channels each having a bandwidth half the predetermined bandwidth of the receiver and the samples in each channel would be taken at a rate corresponding to the predetermined bandwidth of the receiver. It follows then that the receiver bandwidth is limited by the sampling rate limits of digital components used in the memory system.